Innate-like T cell lineages contribute to host defense against pathogens at mucosal barriers. However, there is a fundamental gap that separates the clinicopathologic relevance of their powerful effector properties from a molecular understanding of their regulation. The major questions arise from the surprising observation that the innate-like effector program is acquired during thymic development, independently of microbial exposure, rather than upon encounter with pathogens. The research has crystallized around the recent finding that the innate-like effector program is directed by a novel transcription factor, promyelocytic leukemia zinc factor (PLZF), which is also responsible for a subset of human leukemias. The long-term goal of these studies is to understand in molecular details the development and the functional program of innate-like T cells. The objective of this application is to define the mechanisms by which PLZF enables the effector properties of innate-like T cells. Our central hypothesis is that PLZF directly or indirectly regulates critical transcription factors that separately or together activate different arms of this effector program. The rationale for thi project is that it will provide unprecedented insight into the molecular interactions that regulate the differentiation of effector programs and, in turn, will allow manipulation of these processes for therapeutic benefit. The proposed hypothesis will be tested by pursuing the following specific aims: 1) to characterize the target genes bound by PLZF, and the resulting changes in epigenetic marks and transcriptional program; 2) to characterize the specific role of key transcription factors in differentiating the effector program. While each aim focuses on different approaches, the data will be integrated to develop a model of the transcriptional network regulating the innate-like effector program. The proposal is innovative because it explores the novel idea that a master transcription factor directs the innate-like effector program, which would signal a major shift in our understanding of the biology of innate-like effector T cells. The proposed research is significant because it will enhance our understanding of lymphocyte effector programs and link specific transcription factors to different arms of this program. The concepts and tools developed will make it possible to develop agents that target distinct components of effector programs and, ultimately, to enhance immunity to a range of microbial pathogens.